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Red-shouldered Ctenucha Moth (Ctenucha rubroscapus)

Detailing the physical features, habits, territorial reach and other identifying qualities of the Red-shouldered Ctenucha Moth

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Image Credit: Gordon S. in Fort Stevens Park, OR
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Image Credit: CL J. in CA
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The Red-shouldered Ctenucha Moth lives on the West Coast where is enjoys life in the sun and an all-natural diet of flowers and grasses.

Updated: 07/09/2021; Authored By Staff Writer; Content ©www.InsectIdentification.org
Bold colors on the Red-shouldered Ctenucha Moth mimic that of wasps. This helps it avoid predators. The blue-black body offsets the bright orange-red hairs on the thorax ('shoulders') and head. Its black wings are tipped with a thin line of white at the bottom edges. This species of moth is only found in the low-elevations of the western U.S.

Adults feed on flowers, but the caterpillars feed on grasses. The caterpillar is black with bits of white and a brown head and rear. Tufts of light gray hairs cover the body and when it prepares to pupate, it encases itself in a 'cage' of hairs. Often seen during the day, this species is active from the beginning of summer to the beginning of autumn. Look for it in the coastal grasses and adjacent meadows and marshes. The mostly black Red-shouldered Bug has bright red edges on its pronotum, the 'shoulder' area of the insect. This vivid red color is also seen in the large eyes, an unusual for most insects. The edges of the abdomen are also red and may or may not be visibly extended from under the wings. Despite the alarm coloration, this insect is not a threat people. It is also scentless, meaning it does not spray a noxious chemical when disturbed like other similar-looking insects.

Like many plant bugs, the Red-shouldered Bug tends to form large congregations around host plants and even seeks winter shelters inside warm houses and buildings. Because many plants in the Soapberry family are food sources for this type of bug, it is sometimes referred to as a type of Soapberry Bug. It seems to be fond of the sweet sap and fruit from various trees, having been seen feeding on figs, plums, and cherry trees. Dead insects and food leftovers from humans are also welcome parts of the Red-Shouldered Bug's diet.

This species can be found on or near host plants during the spring, summer and autumn. In warmer regions, a female can produce two broods a year. It is seen almost year round in California, Florida, Texas and Mexico.

General Characteristics
Capability, Shape, Texture/Pattern, Benefits, Dangers
Flying insect icon


Taxonomic Hierarchy
Species Breakdown
Kingdom: Animalia
  Phylum: Arthropoda
    Class: Insecta
      Order: Lepidoptera
        Family: Erebidae
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          Genus: Ctenucha
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            Species: rubroscapus
Identifying Information
Size, Colors, Features
Scientific Name: Ctenucha rubroscapus
Category: Butterfly or Moth
Size (Adult; Length): 15mm to 20mm (0.59" to 0.78")
Colorwheel Graphic Colors: black, red, orange, blue, white
Descriptors: flying, bee, wasp, large, tipped

Relative Size Comparison
Typical Size Between 15mm (0.6in) and 20mm (0.8in)
Lo: 15mm
Md: 17.5mm
Hi: 20mm
Territorial Map*
U.S., Canada, and Mexico
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Prince Edward Is.  
* MAP NOTES: The territorial heat map above showcases (in red) the states and territories of North America where the Red-shouldered Ctenucha Moth may be found (but is not limited to). This sort of data is useful when attempting to see concentrations of particular species across the continent as well as revealing possible migratory patterns over a species' given lifespan. Some insects are naturally confined by environment, weather, mating habits, food resources and the like while others see widespread expansion across most, or all, of North America. States/Territories shown above are a general indicator of areas inhabited by the Red-shouldered Ctenucha Moth. Insects generally go where they please, typically driven by diet, environmental changes, and / or mating habits.


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